1. Field of the Invention
The invention relates generally to the field of drilling wellbores through subterranean formations. More specifically, the invention relates to devices capable of inserting instruments through drill bits used to perform certain operations in subterranean formations below the drill bit.
2. Description of the Related Art
During wellbore drilling operation, it is occasionally desirable to perform operations other than actual drilling into the formation. For instance, when drilling into a fractured or porous zone, it may be desirable to cure losses and to maintain formation strength by injecting cement and/or lost circulation material into the formation. Another example is setting a cement plug for abandonment of a well or well section, possibly followed by drilling of a branched well section. These non-drilling operations occur during the construction of a wellbore or borehole, but typically involve the use of well tools other than a drill bit. Using a drill bit for such non-drilling operations would be undesirable because, for example, attempting to pump a fluid of high density or viscosity and/or comprising coarse material through the drill string with a drill bit attached has been found to be detrimental. This is because conventional drill bits such as polycrystalline diamond cutter (PDC) bits or roller cone bits are provided with bit nozzles for discharging fluid from within a drill string into the wellbore. Such fluids create a substantial risk for the nozzles to plug up due to the high shear, rapid pressure drop, and small orifices. Nozzles normally comprise a nozzle channel with a nozzle insert, and the orifice could in principle be increased by removing the nozzle inserts from the bit. This option is however not seriously contemplated in practice because it would significantly impair the performance of the bit for progressing into the formation. Other operations such as setting a cement plug may simply not be possible with a drill bit and may require other tools.
Therefore, the drill bit is typically removed from the drill string and is replaced by a suitable tool to perform non-drilling operations. For example, when injecting fluids, a tool is used with a sufficiently large orifice in order that fluid can be introduced. This most often means that the drill string is pulled from the borehole. Before pulling the drill string out of the borehole, it is often necessary to first temporarily stabilize the borehole by introducing lost circulation material. This stabilization may often be accomplished through ports in the lower part if the drill string above the drill bit that can be opened and closed again, for example in a circulating sub. Introducing lost circulation material via the circulating sub can plug the annulus between the borehole wall and the lower part of the drill string including the drill bit, so as to require removal of the entire drill string, which may further complicate operations. The pumping of cement through the same ports is not a practical option, as a significant risk exists that the lower part of the drill string including the drill bit could be cemented in place. When the drill string then has been fully removed, the drill bit may be replaced by a cementing stinger. When the drill string is lowered again in the borehole to the desired depth, fluid can be introduced into the borehole. If it is further drilling is desired, the drill string must then be pulled from the borehole hole, so that the drill bit can be remounted.
Most procedures that involve removing the drill bit from the borehole are time-consuming and therefore often quite expensive. Typically, to remove the drill bit from the borehole, the drill string must be withdrawn from the borehole, the pipe string disassembled, then the pipe string reassembled and the drill string run back into the borehole. The foregoing process may take several hours or more depending on the depth of the borehole, among other factors. Moreover, removing the drill bit and drill string from an unstable borehole may result in borehole collapse. In these situations, it may be undesirable to remove the drill string from the borehole.
Other applications for inserting an instrument through a drill bit include the use of “well logging” devices. Well logging devices include one or more sensors for measuring one or more physical parameters of the formations outside the wellbore and/or various parameters of the wellbore itself such as geodetic trajectory. The sensors are disposed in a housing configured to move along the interior of the wellbore. In certain cases, it is difficult to insert well logging instruments into portions of the wellbore due to, for example, high inclination of the wellbore from vertical or rough surface of the wellbore wall. In such cases it is desirable to dispose the drill string within such portions to provide a conduit or passage for the well logging instrument. The instrument may be exposed to the open wellbore by opening a passage in the drill bit, such as by removing a releasable insert, and moving the instrument through the opening.
Previous devices to address the needs described above include providing a drill bit insert in the drill bit which is held in place by means of a ball-latch mechanism, detaching the drill bit insert through the use of a tool inserted into the drill string which is configured to unlatch the ball-latch mechanism, and deploying the tool through the opening in the drill bit created by removing the insert from the bit body. After completion of the task, the tool is then retracted and drill bit insert reattached to the drill bit by means of re-latching the ball-latch mechanism. The drilling activity could then re-commence. However, the foregoing drill bit with an insert does not include the use of a latch mechanism in a sealed enclosure. Drilling mud and other fluids are capable of reaching the latch mechanism in such a situation and rendering it inoperable or causing the mechanism to spontaneously unlatch. Further, in the foregoing drill bits with inserts, the tool used to disengage the latching mechanism does not lock into the latching mechanism, allowing incomplete or misaligned attempts at unlatching the latching mechanism, or worse, release of the insert from the drill bit without its positive connection to the release tool. In such cases, the insert could fall to the bottom of the well, resulting in a difficult and expensive operation to retrieve the insert.
Accordingly, there exists a need for a drill bit and release tool or “running tool” that address one or more disadvantages of the prior art.